c 2008. Astronomical Society of Japan. A Comparative Study of Size Distributions for

We examined the size distributions of small L4 and L5 Jovian Trojan asteroids detected in the Subaru main belt asteroid survey (SMBAS). This was the first attempt to make a comparison of the size distribution between the L4 and L5 Trojans for sizes ranging from 1 km to 10 km, using the results of systematic surveys. We detected 51 L4 Trojans and 62 L5 Trojans ranging from 0.7 km to 13 km in diameter (D) (assuming an albedo of 0.04). We found that there is a difference of the cumulative size distribution between the L4 and L5 populations. The slopes of the cumulative size distribution of the L4 population with 2 km<D< 5 km and 5 km<D< 10 km were 1.3˙0.1 and 2.4 ˙0.1, respectively; meanwhile, that of the L5 population with 2 km<D< 5 km was 2:1 ˙ 0:3. For both populations, we also give composite size distributions covering a range of 5 km<D< 100 km, whose mean slopes are found to be 2.2˙0.1 for L4 and 2.1˙0.1 for L5. Key words: minor planets, asteroids — solar system: general — surveys 1